crontab

CRONTAB(1)                        User Commands                       CRONTAB(1)



NAME
       crontab - maintains crontab files for individual users

SYNOPSIS
       crontab [-u user] <file | ->
       crontab [-u user] <-l | -r | -e> [-i] [-s]
       crontab -n [ hostname ]
       crontab -c
       crontab -V

DESCRIPTION
       Crontab is the program used to install a crontab table file, remove or
       list the existing tables used to serve the cron(8) daemon.  Each user can
       have their own crontab, and though these are files in /var/spool/, they
       are not intended to be edited directly.  For SELinux in MLS mode, you can
       define more crontabs for each range.  For more information, see
       selinux(8).

       In this version of Cron it is possible to use a network-mounted shared
       /var/spool/cron across a cluster of hosts and specify that only one of
       the hosts should run the crontab jobs in the particular directory at any
       one time.  You may also use crontab from any of these hosts to edit the
       same shared set of crontab files, and to set and query which host should
       run the crontab jobs.

       Scheduling cron jobs with crontab can be allowed or disallowed for
       different users.  For this purpose, use the cron.allow and cron.deny
       files.  If the cron.allow file exists, a user must be listed in it to be
       allowed to use crontab.  If the cron.allow file does not exist but the
       cron.deny file does exist, then a user must not be listed in the
       cron.deny file in order to use crontab.  If neither of these files exist,
       then only the super user is allowed to use crontab.

       Another way to restrict the scheduling of cron jobs beyond crontab is to
       use PAM authentication in /etc/security/access.conf to set up users,
       which are allowed or disallowed to use crontab or modify system cron jobs
       in the /etc/cron.d/ directory.

       The temporary directory can be set in an environment variable.  If it is
       not set by the user, the /tmp directory is used.

OPTIONS
       -u     Specifies the name of the user whose crontab is to be modified.
              If this option is not used, crontab examines "your" crontab, i.e.,
              the crontab of the person executing the command. If no crontab
              exists for a particular user, it is created for them the first
              time the crontab -u command is used under their username.

       -l     Displays the current crontab on standard output.

       -r     Removes the current crontab.

       -e     Edits the current crontab using the editor specified by the VISUAL
              or EDITOR environment variables.  After you exit from the editor,
              the modified crontab will be installed automatically.

       -i     This option modifies the -r option to prompt the user for a 'y/Y'
              response before actually removing the crontab.

       -s     Appends the current SELinux security context string as an
              MLS_LEVEL setting to the crontab file before editing / replacement
              occurs - see the documentation of MLS_LEVEL in crontab(5).

       -n     This option is relevant only if cron(8) was started with the -c
              option, to enable clustering support.  It is used to set the host
              in the cluster which should run the jobs specified in the crontab
              files in the /var/spool/cron directory.  If a hostname is
              supplied, the host whose hostname returned by gethostname(2)
              matches the supplied hostname, will be selected to run the
              selected cron jobs subsequently.  If there is no host in the
              cluster matching the supplied hostname, or you explicitly specify
              an empty hostname, then the selected jobs will not be run at all.
              If the hostname is omitted, the name of the local host returned by
              gethostname(2) is used.  Using this option has no effect on the
              /etc/crontab file and the files in the /etc/cron.d directory,
              which are always run, and considered host-specific.  For more
              information on clustering support, see cron(8).

       -c     This option is only relevant if cron(8) was started with the -c
              option, to enable clustering support.  It is used to query which
              host in the cluster is currently set to run the jobs specified in
              the crontab files in the directory /var/spool/cron , as set using
              the -n option.

       -V     Print version and exit.

CAVEATS
       The files cron.allow and cron.deny cannot be used to restrict the
       execution of cron jobs; they only restrict the use of crontab.  In
       particular, restricting access to crontab has no effect on an existing
       crontab of a user. Its jobs will continue to be executed until the
       crontab is removed.

       The files cron.allow and cron.deny must be readable by the user invoking
       crontab.  If this is not the case, then they are treated as non-existent.

SEE ALSO
       crontab(5), cron(8)

FILES
       /etc/cron.allow
       /etc/cron.deny

STANDARDS
       The crontab command conforms to IEEE Std1003.2-1992 (``POSIX'') with one
       exception: For replacing the current crontab with data from standard
       input the - has to be specified on the command line.  This new command
       syntax differs from previous versions of Vixie Cron, as well as from the
       classic SVR3 syntax.

DIAGNOSTICS
       An informative usage message appears if you run a crontab with a faulty
       command defined in it.

AUTHOR
       Paul Vixie ⟨vixie@isc.org⟩
       Colin Dean ⟨colin@colin-dean.org⟩



cronie                             2019-10-29                         CRONTAB(1)